A conventional bicycle seat post is generally made as a cylindrical metal tube and the saddle is connected to an end of the seat post. The seat post is inserted in the seat tube of bicycle frame and a clamping device clamps the open end of the seat tube of the bicycle frame so as to position the seat post in the seat tube of the bicycle frame. The saddle supports the weight of the rider so that the clamping device has to securely tighten the open end of the seat tube so as to keep the seat post from sliding in the seat tube. The stress of concentration is located at the portion of the seat post contacting the open end of the seat tube. The seat post in the seat tube is stiff and does not have any flexibility to absorb the inward clamping force applied by the clamping device such that the seat post could be damaged or cracked by the force.
The present invention intends to provide a seat post that includes two arcuate plates and a reinforcement rib which is sandwiched between the two arcuate plates so as to obtain better strength.